1. Field of the Invention
The invention relates to fluid-operated brake actuators for vehicles and, more particularly, to a fluid-operated actuator with a sealed chamber and a method for sealing the chamber.
2. State of the Prior Art
An air brake system for a vehicle such as a bus, truck or the like typically includes a brake shoe and drum assembly actuated by an air-operated brake actuator. Conventional air brake actuators have both a service brake actuator for actuating the brakes under normal driving conditions by the application of compressed air and an emergency or spring brake actuator that actuates the brakes when air pressure has been released. The spring brake actuator includes a large-force compression spring that is compressed by the pressurized air and expands to apply the brakes when the air is released. Typically, the spring brake actuator is disposed in tandem with the service brake actuator.
The spring brake actuator typically comprises a housing formed by opposing cup-shaped housing portions. The housing is divided into two chambers by a diaphragm, whose peripheral edge is compressed between the housing portions, with the spring in one of the chambers (the spring chamber) acting between an end wall of the spring brake housing and a pressure plate abutting the diaphragm. When air pressure is applied to the opposite chamber (the pressure chamber), air pressure acting against the diaphragm and pressure plate compresses the spring.
In tandem actuator assemblies, a spring brake push rod typically extends from the pressure plate/diaphragm assembly in the spring brake actuator portion, through an aperture in a wall separating the spring brake actuator from the service brake actuator, and into a chamber in the service brake. In many applications, the spring brake actuator rod is held retracted against the pressure plate/diaphragm assembly by a relatively small return spring. In newer applications, the spring brake actuator rod is integral with the pressure plate and held in a retracted position by the air pressure. For each design, the spring brake actuator rod does not affect the normal operation of the brake.
The service chamber is typically divided into two chambers by a second diaphragm. Depressing the brake pedal during normal driving operation introduces compressed air into one of the chambers of the service brake actuator which, acting against the second diaphragm, causes a service brake push rod on the other side of the diaphragm to extend and apply the brakes with an application force proportional to the air pressure in the service brake actuator.
In the event of a loss of air pressure or an intentional exhaustion of air from the spring brake actuator, the large-force compression spring expands to extend the spring brake actuator rod which, in turn, extends the service brake push rod to apply the brakes. Thus, the spring brake portion serves both as a parking brake and as an emergency brake.
Because a large-force spring is necessary to actuate the brakes in the case of an accidental loss of pressure or the purposeful depressurization for a parking brake, the housing portions containing the large-force spring must be securely held together for normal operation and to avoid injury from dislocation of the housing portions under the force of the spring. Further, the attachment of the housing portions must dissuade tampering, such as by unqualified mechanics, because the large-force spring will cause injury if it is not properly caged prior to servicing. Finally, the joint coupling the housing portions should accommodate a sealed mounting of the diaphragm, which is conventionally mounted between the housing portions and also provides a sealed attachment of the housing portions.
Some prior designs have attempted to address the problem of reducing or eliminating the risk of injury to persons or dislocation of housing portions by continuously rolling a lip of one housing portion about a lip of the other with the diaphragm therebetween, whereby the assembled housing is sealed and cannot be disassembled without destruction. While the joint is strong enough to contain the spring, it is expensive to manufacture.
The invention relates to an air-operated brake actuator for applying the brakes of a vehicle comprising first and second housing sections between which is sandwiched a diaphragm. The first housing section comprises a first end wall, a first peripheral side wall extending away from the first end wall to define a first interior cavity. An edge surface is provided on an outer exterior of the first peripheral side wall, and an indentation is formed within at least a portion of the edge surface. The second housing section comprising a second end wall and a second peripheral side wall extending away from the second end wall to define a second interior cavity adjacent the diaphragm. A portion of the second peripheral side wall and first peripheral side wall sandwich a circumferential edge portion of the diaphragm. The second peripheral side wall has an end portion that overlaps the edge surface and the indentation and further has at least one projection extending into the indentation to secure the second housing section to the first housing section with the diaphragm sealingly clamped therebetween whereby the second housing section cannot be separated from the first housing section without deforming the second housing section.
Preferably, the edge surface further comprises a groove in which is received a portion of the diaphragm circumferential edge and the diaphragm includes a bead received in the edge surface groove. The first peripheral side wall includes a radially extending lip that terminates in the edge surface and the second peripheral side wall end portion is generally parallel to the edge surface to sandwich the diaphragm between the edge surface and the second peripheral side wall end portion. The indentation can be a continuous or discontinuous groove and the projection can be multiple deformations, such as punches or bent portions, received within the groove.